The regeneration of injured nerves is a significant subject in neurobiology. Nerve regeneration may activate the neurons at the injured points to grow through some guidance channels to connect the upper and lower nerve channels again. Recently, Anderson's group (UC Irvine, USA) has used adult human neural stem cells to regenerate injured spinal cord tissue and improve the mobility in mice. (PNAS, Sep. 27, 2005). However, there are still some problems left.
In their experiments, they injected human stem cells into the spinal cord of a mouse after it had been injured for 9 days. The problem with this approach is determining the valid waiting period to inject stem cells into a human body, because it is unknown how long 9 days for mice may be for a human. For example, it took 4 months for the mice to crawl. How many days does this equal for a human?
During the feeding, the mice's immune system was controlled. This may present some serious problems when the same method is applied to the human body.
Other experiments showed that, this method may be invalid to those spinal cords which have been injured for longer than 6 months. These factors show that even with the help of human neural stem cells there is still a long way to realize the functional regeneration of injured human spinal cords. Accordingly, it may be advantageous to provide additional methods to lead signals from a nerve fiber from one end to the other.